The present invention relates to a clothes dryer control system for detecting blockages in the dryer exhaust vent ducting.
The installation of a customer""s clothes dryer exhaust vent ducting is critical to the performance of the clothes drying appliance. Ducting that is either too long, has too many bends or is made of very flexible material can choke the airflow coming out of the dryer and thereby cause a reduction of the total system airflow speed through the drying chamber and out the exhaust vent ducting. This reduction in airflow speed causes inefficient operation of the clothes dryer heater system and may result in increased drying times for all types of loads and fabrics.
Clothes dryers currently utilize thermistors and electronic controls to monitor and control drying time and degree of dryness of clothes during different drying cycles. U.S Pat. No. 5,291,667 issued Mar. 8, 1994 and U.S. Pat. No. 5,444,924 issued Aug. 29, 1995 disclose a method of controlling a dryer by monitoring the air inlet temperature. When the monitored temperature exceeds a high limit temperature value a given number of times the dyer activates a blockage indicator.
While the use of an inlet temperature thermistor or thermostat to detect temperatures above a high limit inlet temperatures causing heaters to turn off is known, there still exist a need for determining the relative air flow restriction in the dryer vent ducting blockage prior to a high limit threshold being reached so as to permit continuous drying operation of the clothes dryer until the air flow restriction is corrected.
The present invention relates to a dryer control system that detects a decrease in airflow speed through the dryer due to an increase in air flow restriction by monitoring the rate of temperature rise at an inlet temperature sensor located upstream of the dryer drum.
Preferably, the control system estimates the equivalent airflow restriction caused by the customer""s exhaust venting installation from temperature signals monitored by the inlet temperature sensor.
In accordance with the present invention there is provided a control system for an automatic clothes dryer having a clothes drying drum, an air inlet to the drum, an air outlet from the drum, means for flowing dryer air through the drum and heater means for heating the dryer air at the air inlet side of the drum. The system comprises a temperature sensor for sensing drum inlet temperature of the dryer air at the inlet side of the drum. The system further comprises a controller responsive to the drum inlet air temperature sensor for determining the time rate of increased change in the drum inlet temperature and generating an air flow blockage signal when the time rate of change of temperature exceeds a predetermined rate value.
Preferably, the inlet temperature sensor is positioned adjacent the heating elements of a clothes dryer and upstream of the drying drum in the direction of air flow through the dryer. The inlet temperature sensor generates a resistance signal that is read by a circuit as a voltage signal which is sent to a controller. The controller converts or transforms the voltage signal by a transfer function into a corresponding temperature value. The temperature values are processed in accordance with a detection algorithm that determines the change in temperature at the inlet temperature sensor position using the input signal from the inlet temperature sensor. The controller relates the rate of temperature change to an equivalent venting exhaust restriction and therefore, information relating to a qualitative evaluation of the customer""s venting setup can be ascertained. This information can be
1) relayed back to the customer if he or she so desires by recalling the value (or qualitative evaluation) using a dryer user interface;
2) used subsequently by the dryer""s controller to adjust displayed estimated drying times as well as to adjust the drying control cycle functions with respect to the customer""s venting setup; and,
3) store the information for field technicians as a quick diagnostic tool.